LogStashLogger

This gem implements a subclass of Ruby's Logger class that logs directly to logstash. It writes to a logstash listener over a UDP (default) or TCP connection, in logstash JSON format. This is an improvement over writing to a file or syslog since logstash can receive the structured data directly.

Features

• Can write directly to logstash over a UDP or TCP/SSL connection.
• Can write to a file, Redis, a unix socket, stdout or stderr.
• Always writes in logstash JSON format.
• Logger can take a string message, a hash, a LogStash::Event, an object, or a JSON string as input.
• Events are automatically populated with message, timestamp, host, and severity.
• Easily integrates with Rails via configuration.

Installation

Add this line to your application's Gemfile:

gem 'logstash-logger'

And then execute:

$ bundle

Or install it yourself as:

$ gem install logstash-logger

Basic Usage

require 'logstash-logger'

# Defaults to UDP on 0.0.0.0
logger = LogStashLogger.new(port: 5228)

# Specify host and type (UDP or TCP) explicitly
udp_logger = LogStashLogger.new(type: :udp, host: 'localhost', port: 5228)
tcp_logger = LogStashLogger.new(type: :tcp, host: 'localhost', port: 5229)

# Other types of loggers
file_logger = LogStashLogger.new(type: :file, path: 'log/development.log', sync: true)
unix_logger = LogStashLogger.new(type: :unix, path: '/tmp/sock')
redis_logger = LogStashLogger.new(type: :redis)
kafka_logger = LogStashLogger.new(type: :kafka)
stdout_logger = LogStashLogger.new(type: :stdout)
stderr_logger = LogStashLogger.new(type: :stderr)
io_logger = LogStashLogger.new(type: :io, io: io)

# Multiple Outputs
multi_logger = LogStashLogger.new([{type: :file, path: 'log/development.log'}, {type: :udp, host: 'localhost', port: 5228}])

# The following messages are written to UDP port 5228:

logger.info 'test'
# {"message":"test","@timestamp":"2014-05-22T09:37:19.204-07:00","@version":"1","severity":"INFO","host":"[hostname]"}

logger.error '{"message": "error"}'
# {"message":"error","@timestamp":"2014-05-22T10:10:55.877-07:00","@version":"1","severity":"ERROR","host":"[hostname]"}

logger.debug message: 'test', foo: 'bar'
# {"message":"test","foo":"bar","@timestamp":"2014-05-22T09:43:24.004-07:00","@version":"1","severity":"DEBUG","host":"[hostname]"}

logger.warn LogStash::Event.new(message: 'test', foo: 'bar')
# {"message":"test","foo":"bar","@timestamp":"2014-05-22T16:44:37.364Z","@version":"1","severity":"WARN","host":"[hostname]"}

# Tagged logging
logger.tagged('foo') { logger.fatal('bar') }
# {"message":"bar","@timestamp":"2014-05-26T20:35:14.685-07:00","@version":"1","severity":"FATAL","host":"[hostname]","tags":["foo"]}

URI Configuration

You can use a URI to configure your logstash logger instead of a hash. This is useful in environments such as Heroku where you may want to read configuration values from the environment. The URI scheme is type://host:port/path. Some sample URI configurations are given below.

udp://localhost:5228
tcp://localhost:5229
unix:///tmp/socket
file:///path/to/file
redis://localhost:6379
kafka://localhost:9092
stdout:/
stderr:/

Pass the URI into your logstash logger like so:

# Read the URI from an environment variable
logger = LogStashLogger.new(uri: ENV['LOGSTASH_URI'])

Logstash Configuration

In order for logstash to correctly receive and parse the events, you will need to configure and run a listener that uses the json_lines codec. For example, to receive events over UDP on port 5228:

input {
  udp {
    host => "0.0.0.0"
    port => 5228
    codec => json_lines
  }
}

See the samples directory for more configuration samples.

SSL

If you are using TCP then there is the option of adding an SSL certificate to the options hash on initialize.

LogStashLogger.new(type: :tcp, port: 5228, ssl_certificate: "/path/to/certificate.crt")

The SSL certificate and key can be generated using

openssl req -x509 -batch -nodes -newkey rsa:2048 -keyout logstash.key -out logstash.crt

You can also enable SSL without a certificate:

LogStashLogger.new(type: :tcp, port: 5228, ssl_enable: true)

The following Logstash configuration is required for SSL:

input {
  tcp {
    host => "0.0.0.0"
    port => 5228
    codec => json_lines
    ssl_enable => true
    ssl_cert => "/path/to/certificate.crt"
    ssl_key => "/path/to/key.key"
  }
}

Custom Log Fields

LogStashLogger by default will log a JSON object with the format below.

{
  "message":"Some Message",
  "@timestamp":"2015-01-29T10:43:32.196-05:00",
  "@version":"1",
  "severity":"INFO",
  "host":"hostname"
}

Some applications may need to attach additional metadata to each message. The LogStash::Event can be manipulated directly by specifying a customize_event block in the LogStashLogger configuration.

config = LogStashLogger.configure do |config|
  config.customize_event do |event|
    event["other_field"] = "some_other_value"
  end
end

This configuration would result in the following output.

{
    "message": "Some Message",
    "@timestamp": "2015-01-29T10:43:32.196-05:00",
    "@version": "1",
    "severity": "INFO",
    "host": "hostname",
    "other_field": "some_other_value"
}

Rails Integration

Verified to work with both Rails 3 and 4.

By default, every Rails log message will be written to logstash in LogStash::Event JSON format.

For minimal, more-structured logstash events, try one of the following gems:

• lograge
• yarder

Currently these gems output a JSON string, which LogStashLogger then parses. Future versions of these gems could potentially have deeper integration with LogStashLogger (e.g. by directly writing LogStash::Event objects).

Rails Configuration

Add the following to your config/environments/production.rb:

Common Options

# Optional, Rails sets the default to :info
config.log_level = :debug

# Optional, Rails 4 defaults to true in development and false in production
config.autoflush_log = true

# Optional, use a URI to configure. Useful on Heroku
config.logstash.uri = ENV['LOGSTASH_URI']

UDP

# Optional, defaults to '0.0.0.0'
config.logstash.host = 'localhost'

# Optional, defaults to :udp.
config.logstash.type = :udp

# Required, the port to connect to
config.logstash.port = 5228

TCP

# Optional, defaults to '0.0.0.0'
config.logstash.host = 'localhost'

# Required, the port to connect to
config.logstash.port = 5228

# Required
config.logstash.type = :tcp

# Optional, enables SSL
config.logstash.ssl_enable = true

Unix Socket

# Required
config.logstash.type = :unix

# Required
config.logstash.path = '/tmp/sock'

Redis

Add the redis gem to your Gemfile:

gem 'redis'

# Required
config.logstash.type = :redis

# Optional, will default to the 'logstash' list
config.logstash.list = 'logstash'

# All other options are passed in to the Redis client
# Supported options include host, port, path, password, url
# Example:

# Optional, Redis will default to localhost
config.logstash.host = 'localhost'

# Optional, Redis will default to port 6379
config.logstash.port = 6379

Kafka

Add the poseidon gem to your Gemfile:

gem 'poseidon'

# Required
config.logstash.type = :kafka

# Optional, will default to the 'logstash' topic
config.logstash.path = 'logstash'

# Optional, will default to the 'logstash-logger' producer
config.logstash.producer = 'logstash-logger'

# Optional, will default to localhost:9092 host/port
config.logstash.hosts = ['localhost:9092']

# Optional, will default to 1s backoff
config.logstash.backoff = 1

File

# Required
config.logstash.type = :file

# Optional, defaults to Rails log path
config.logstash.path = 'log/production.log'

IO

# Required
config.logstash.type = :io

# Required
config.logstash.io = io

Multiple Outputs

config.logstash = [
  {
    type: :file,
    path: 'log/production.log'
  },
  {
    type: :udp,
    port: 5228,
    host: 'localhost'
  }
]

Logging HTTP request data

In web applications, you can log data from HTTP requests (such as headers) using the RequestStore middleware. The following example assumes Rails.

# in Gemfile
gem 'request_store'

# in application.rb
LogStashLogger.configure do |config|
  config.customize_event do |event|
    event["session_id"] = RequestStore.store[:load_balancer_session_id]
  end
end

# in app/controllers/application_controller.rb
before_filter :track_load_balancer_session_id

def track_load_balancer_session_id
  RequestStore.store[:load_balancer_session_id] = request.headers["X-LOADBALANCER-SESSIONID"]
end

Ruby Compatibility

Verified to work with:

• MRI Ruby 1.9.3, 2.0.x, 2.1.x, 2.2.x
• JRuby 1.7+
• Rubinius 2.2+

Ruby 1.8.7 is not supported.

What type of logger should I use?

It depends on your specific needs, but most applications should use the default (UDP). Here are the advantages and disadvantages of each type:

• UDP is faster than TCP because it's asynchronous (fire-and-forget). However, this means that log messages could get dropped. This is okay for many applications.
• TCP verifies that every message has been received via two-way communication. It also supports SSL for secure transmission of log messages over a network. This could slow your app down to a crawl if the TCP listener is under heavy load.
• A file is simple to use, but you will have to worry about log rotation and running out of disk space.
• Writing to a Unix socket is faster than writing to a TCP or UDP port, but only works locally.
• Writing to Redis is good for distributed setups that generate tons of logs. However, you will have another moving part and have to worry about Redis running out of memory.
• Writing to stdout is only recommended for debugging purposes.

For a more detailed discussion of UDP vs TCP, I recommend reading this article: UDP vs. TCP

Troubleshooting

JSON::GeneratorError

Your application is probably attempting to log data that is not encoded in a valid way. When this happens, Ruby's standard JSON library will raise an exception. You may be able to overcome this by swapping out a different JSON encoder such as Oj. Use the oj_mimic_json gem to use Oj for JSON generation.

No logs getting sent on Heroku

Heroku recommends installing the rails_12factor so that logs get sent to STDOUT. Unfortunately, this overrides LogStashLogger, preventing logs from being sent to their configured destination. The solution is to remove rails_12factor from your Gemfile.

Logging eventually stops in production

This is most likely not a problem with LogStashLogger, but rather a different gem changing the log level of Rails.logger. This is especially likely if you're using a threaded server such as Puma, since gems often change the log level of Rails.logger in a non thread-safe way. See #17 for more information.

Breaking changes

Version 0.5+

• The source event key has been replaced with host to better match the latest logstash.
• The (host, port, type) constructor has been deprecated in favor of an options hash constructor.

Version 0.4+

LogStash::Event uses the v1 format starting version 1.2+. If you're using the v1, you'll need to install LogStashLogger version 0.4+. This is not backwards compatible with the old LogStash::Event v1.1.5, which uses the v0 format.

Version 0.3+

Earlier versions of this gem (<= 0.2.1) only implemented a TCP connection. Newer versions (>= 0.3) also implement UDP, and use that as the new default. Please be aware if you are using the default constructor and still require TCP, you should add an additional argument:

# Now defaults to UDP instead of TCP
logger = LogStashLogger.new('localhost', 5228)
# Explicitly specify TCP instead of UDP
logger = LogStashLogger.new('localhost', 5228, :tcp)

Contributors

• David Butler
• pctj101
• Gary Rennie
• Nick Ethier
• Arron Mabrey
• Jan Schulte
• Kurt Preston
• Chris Blatchley
• Felix Bechstein
• Vadim Kazakov
• Anil Rhemtulla

Contributing

1. Fork it
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create new Pull Request